Television system



April 1942- v. K. zwoRYKm 2,280,877

TELEVISION SYSTEM Filed Nov. 26, 1958 s Sheet-Sheet 2 Wmassss: 3 INVENTOR WWM Vladimir KZworykiu April 28, 1942. V.'K. ZWORYKIN TELEVISION SYSTEM 3 Sheefs-Sheet 3 Filed Nov. 26, 1938 n S WITNESSES:

INVENTOR Vladimir KZworykin.

ATTORNE MWM @u 4. W

Patented Apr. 28, 1942 TELEVISION SYSTEM Vladimir K. Zworykin, Forest Hills, N. Y., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application November 26,v 1938, Serial No. 242,505

2 Claims.

My invention relates, in general, to television systems.

This application is a continuation-in-part of my application Serial No. 683,337, filed December 29, 1923 now Patent No. 2,141,059. Certain subject-matter herein disclosed is claimed in my aforesaid patent and in my applications Serial Nos. 448,834, filed May 1,1930, and 254,607, filed February 4, 1939.

One of the objects of my invention is to provide a system for enabling a person to see distant moving objects or views by radio.

Another object of my invention is to eliminate synchronizing devices heretofore employed in television systems.

Still another object of my invention is to provide a system for broadcasting, from a central point, moving pictures, scenes from plays, or similar entertainments.

The above and other objects of my invention will be explained more fully hereinafter with reference to the accompanying drawings forming a part of this specification.

Referring now to the drawings,

Figure 1 is a diagramof a station for broadcasting motion pictures or other visual indications, and may be considered the television transmitter;

an amplifier triode 5. The grid of the amplifier is connected through a transformer 6 to the Fig. 2. is a diagram of a receiving station for receiving the scenes broadcasted from the transmitting station;

Fig. 3 is a fragmentary view of an alternative arrangement for the transmitting station;

Fig. 4- shows an arrangement whereby the control of the transmitting and the receiving stations may be exercised from a central station;

Fig. 5 shows the circuits of the transmitting station when a central station is used; and

Fig. 6 is another modification of my invention.

Both of these stations are shown by means of conventional circuit and apparatus diagrams in sufllcient detail to enable the invention to be readily explained and understood.

Any visual indications may be broadcasted by the transmitting set I consisting of apparatus and circuits and be received by the receiving set 2 consisting of apparatus and circuits.

The apparatus of the transmitting set I comprises an antenna system 3 which is so tuned that it may oscillate at two separate and distinct frequencies. The oscillating circuit including the antenna 3 is connected on one side by means of a transformer 4 to the plate circuit of hoIe so cut therein as to form the cathode ray plate circuits of modulator triodes land 8, An oscillator triode 9 is connected through a transformer III to the grid circuit of the modulator triodes 1 and I. The above arrangement oomprises what is known as an ordinary push-andpull" transmitting arrangement.

By means of a transformer II, the plate circuit of an amplifier I2 is also connected to the grid circuits of the modulator triodes 1 and 3.

The oscillating circuit comprising the antenna 3 is also connected, by means of a transformer l3, to the plate circuit of an amplifier triode M. The grid circuit of the amplifier I4 is connected, by means of a transformer ii, to the plate circuits of modulator triodes l6 and I1. An oscillator triode I8 is connected, by means of a transformer Hi, to the grid circuits of the modulator triodes l6- and i1. By means of transformers and 2|, alternating-current generators 22 and 23 are also connected to the grid circuits of the modulator triodes l6 and I1.

- The generator 22 is so constructed as to generate high-frequency alternating current of a frequency of about 1000.cyc1es, while the alternating-current generator 23 is adapted to generate an alternating current of a frequency at about 16 cycles.

It is, of course, obvious that triodes connected in oscillating circuits may be used in place of the alternating-current generators 22 and 23.

The plates 25 and 26 in a cathode-ray tube 21 are connected in the circuit through a series transformer 24. Coils 28 and 29 are associated with the cathode-ray tube 21 in such position that the magnetic fleld which may be produced by said coils is parallel to the electrostatic field which may be generated by the plates 25 and 26, and these coils are connected in circuit with the alternating-current generator 23.

The cathode-ray tube 21 is similar in some respects to the ordinary cathode-ray oscillograph and has a hot cathode 29', a diaphragm 30 and tubular anode 3|. The diaphragm 30 has a small into a thin beam.

In place of the ordinary fluorescent screen is substituted a composite plate 32 having layers of different material. If the tube 21 has the usual low pressure gas, such as argon, the gas pressure will be substantially equal on the two sides of the plate 32. This is because the plate 32 is permeable to gas. It comprises a sheet 34 of aluminum foil on the face next the cathode fluorescent screen 60.

ray. The foil must be thin enough to be readily penetrated by the cathode ray. It is as thin as it can be and satisfactorily support a layer 35 of aluminum oxide, The layer of aluminum oxide is as thin as it can be and still insulate a layer 36 of photoelectric material from the aluminum foil. The combined thickness of the whore plate 32 need not exceed one half mil.

Preferably the photoelectric material is potas-- sium hydride, deposited in such a manner that'it is in theform of small globules, each separated from its neighbor and insulated therefrom by the aluminum oxide.

A lens 31! or system of lenses is secured in place by means of a frame 38 disposed at the end of the cathode-ray tube. The lens 31 is arranged to focus the image or scene to be observed upon the photoelectric material of the composite plate 32. A grid 39 is placed at some distance in front of the composite plate 32 and is connected to the grid of the amplifier triode II. A high potential is applied to the anode II by a rectifier 40 which is supplied with current from .an alternatingcurrent source 4|.

In the receiving device 2 in Fig. 2, an oscillating circuit 50, including an antenna 5|, is adapted to be resonant to current of two distinct frequencies, these frequencies being the frequencies generated by the oscillating circuits that include the triodes 9 and it of the transmitting set. An amplifier triode 53 is connected to the oscillating circuit 50., The plate circuit of the amplifier triode 53 is connected to a grid 54 in a cathode-ray tube 55.

The cathode-ray tube 55 is constructed in a manner similar to the ordinary cathode-ray oscillograph and comprises a hot cathode 56, the

grid 54, a tubular anode 51, plates 58 and 59 that are used to set up an electrostatic field and a The anode 51 of the cathode-ray tube 55 is supplied with high voltage by the operation'of a rectifier 6 I that rectifies the alternating current supplied by a source of alternating current.

The oscillating circuit 50 is also connected by means of a transformer 53 with a circuit 64. The circuit 64 is, in turn, connected by means of V transformers 55 and 55 with the grid circuit of the amplifier triodes Gland 58. The plate circult of the amplifier triode 81 is connected with the plates 58 and 59 of the cathode-ray tube 55 while the circuit of the amplifier triode 58 is connected to the coils 69 and 10 that are associated with the cathode-ray tube 55 and so disposed with respect thereto that the magnetic fields generated by the coils are parallel to the electrostatic field generated by the plates 58 and 59. i

The transformer 65 is so constructed that it acts as a wave trap for the particular high frequency that is generated by the generator 22 at the transmitting station so as to eliminate this frequency from the circuit 84. In a like manner,

the photoelectric'cell and the cathode-ray tube arranged to focus the light'fromthe fluorescent screen on the cell. A diapositive or ordinary photographic negative 18, that. has the image on it that it is desired to transmit, is placed between the lens and the cathode-ray tube. The circuit connections of this arrangement are similar to those shown in Fig. 1; 1

The apparatus shown in Fig. 4 is practically identical with the apparatus shown at the right in Fig. 1, with the exception that there is provided a separate antenna M3 and includes means whereby the synchronizing frequencies generated by the generators i112 and I23 may be radiated from a central station.

Fig. 5 is very similar to Fig.1, with the exception that the coils I09 and H0 for creating the electromagnetic field for controlling the cathode beam and the plates Ill and H2 for creating the electrostatic field are controlled by detector triodes I01 and I08 which are connected to the receiving antenna through the oscillatory circuit Illl.

Having briefly described the apparatus shown in the drawings, I will now explain its detailed operation. For this purpose it will be assumed, that it is desired to broadcast the image of some object which is in front of the lens 31 associated with the transmitting cathode ray tube 21.

Ordinarily the oscillations'generated by the oscillator 9 are not radiated by the antenna 3. This is because of the fact that these oscillations are neutralized by the action of the modulator triodes I and 8, and, consequently, there is no transfer of energy into the secondary of transformer 5. The only manner in which the antenna can be set in oscillation by the operation of the the transformer 56 acts as a wave trap for the particular frequency generated'by the generator 23 by the transmitting station.

The alternative arrangement of the apparatus in the transmitting station, shown in Fig. 3, is

to the oscillograph. A lens 11 is disposed between.

triode 9 is by a change in condition in the primary of the transformer II which is connected to the grid 39 and to the aluminum foil 34 of the composite plate $2.

The light from the image placed before the lens 31 is so varied that, upon the focusing of this light upon the photoelectric globules 36 of the composite plate 32, electron emission of varying .intensity by these particles takes place in acplate 33, even though the photoelectric globules emit electrons. When the cathode beam strikes a particular point upon the aluminum foil, it is of sufficient intensity to penetrate it, as well as the aluminum oxide. The action of the cathode ray on the aluminum oxide in its path, particularly in the presence of the gas, is to produce a conductive connection between the aluminum plate 34 and the particular globule or globules of potassium hydride in the path of the cathode ray. The electrons emitted by these globules are therefore subjected to the field produced by the battery 42 acting across the conductive part of the aluminum oxide. The amount of the emission will depend upon the degree of illumination of these globules. The current flowing in the circuit is dependent upon the electron emission from the globule or globules covered by the cathode beam. This current is amplified by means of the amplifier triode l2. The current from the grid 39 to the grid of the tube 12 is so small that no grid leak is necessary for the tube l2 although one may be supplied if desired. The output of the amplifier l2 nowcauses the modulator triodes 1 and 8 to transmit, through the transformer 6, the high-frequency oscillations, generated by the oscillator triode 9, modulated in accordance with the current in the amplifier triode I2 which, in turn, is governed by the intensity of the light focused upon the particular spot at which the cathode ray is located. The intensity of this electron stream is, of course, governed by the intensity of the light from the object.

As previously mentioned, the alternating-current generators 22 and 23 are producing alternating current of a high and low frequency, respectively. By the operation of the modulator triodes l6 and H, the oscillations produced by the oscillator triode I8 are modulated in accordance with both the frequency of the alternating-current generated by the generator 22 and the alternating current generated by the generator 23. Thi modulated high frequency current is amplified by the amplifier triode l4 and radiated by the antenna 3.

As the output of the alternating-current generator 22 is also connected to the plates 25 and 26 in the cathode-ray tube 21, an electrostatic field is set up by these plates which varies in accordance with the frequency of the current generatedby the generator 22. As this electrostatic field varies, the electrostatic action upon the electrode beam causes it to be swung from one edge of the composite plate 32 to the other.

A portion of the alternating current generated by the generator 23 also traverses the coils 23 and 29 which, as before mentioned, are so positioned with respect to the cathode tube 21 that the magnetic field generated by these coils is parallel to the electrostatic field generated by plates 25 and 26. The varying magnetic field set up by these coils tends to cause the cathoderay beam to traverse the plate 35 in a direction at right angles to that before described.

The resultant action between the magnetic fields and the electrostatic fields upon the oathode beam is such that the beam covers every point in the whole area of the composite plate 32 in of a second, that is, in cycle of the frequency generated by the alternating-current generator 23. Thus, in of a second, the cathode beam traverses the surface of the composite plate twice.

As the cathode beam traverses the surface of the composite plate 32 point by point in a definite sequence, there is a current flowing from the grid 39 and the aluminum foil 34 at each particular point, and this current is directly proportional to the intensity of light from the object to be observed. Thus. the oscillatory current generated by the oscillator triode 9 is modulated in accordance with the light from each portion of the image.

At the receiving station, the modulated oscillatory currents generated by the oscillator 9 of the transmitter are received by the antenna and transferred to the detector triode 53 through the transformer 52. The detector triode 53 then operates to detect the modulations and then these are transferred through its plate circuit to the grid 54 of the cathode-ray tube 55.

By means of the transformer 63, associated with the oscillating circuit 56, the modulated radio-frequency current generated by oscillator I8 is received and transferred by transformer 65 and 66 in the detector triodes 61 and 66. By the operation of the transformer 65, only the radio frequency that is modulated by the generator 22 is detected. In a like manner, by the operation'of the transformer 66, only the radio frequency modulated by the generator 23 is received by the detector triode 68.

As the plate circuit of the detector triode 61 is connected to the plates 58 and 59 in the cathoderay oscillograph 55, an electrostatic field is set up by these plates which varies in identically the same manner as the electrostatic field generated by the plates 25 and 26 in the transmitting cathode-ray tube. Likewise, the plate circuit of the triode 68 is connected'to the coils 69 and 16 which generate a magnetic field parallel to the electrostatic field generated by the plates 56 and 59 and that varies in exactly the same manner as the magnetic field set up by the coils Hand 29 at the transmitting station. Thus, when the cathode-ray beam passes through the grid 54 and the anode 51 to the fluorescent screen 66, it is caused to traverse a path' in accordance with the resultant magnetic and electrostatic fields set up. Therefore, the cathode-ray beam traverses the whole area of the fluorescent screen once in of a second, or twice 'ln of a second, in the same manner as the cathode beam in the cathode-ray tube 21 at the transmitting station.

When the cathode beam in the cathode-ray tube of the transmitter is in a certain particular position, the oscillatory current generated by the oscillator 9 is modulated in accordance with the intensity of the light falling upon that particular point. This modulated current is radiated by the antenna 3 and received by the antenna 5| at the receiving station. At this particular point, the cathode beam in the cathode-ray tube will be in the same relative position as the cathode beam at the sending station. By the action of the grid 54, the intensity of the cathode ray reaching the fluorescent screen at this particular point is varied in accordance with the light from the image at the transmitting station.

Thus, for every particular point on the image the carrier current radiated by the antenna 3 is modulated whereby the potential on the grid 54 of the receiving cathode ray tube 55 is varied, as is also the intensity of fluorescence of the particular point upon the fluorescent screen 56.

As the whole, area of the composite plate 32 at the transmitting station and the fluorescent screen 66 at the receiving station is covered by the cathode beams in of a second, the image of the object will be displayed on the screen 66 during V42 of a second. However, as the frequency of the oscillation of the generator 23 is 16 cycles per second, the picture will be transmitted twice and will remain on the screen 66 during ,4 of a second. Thus, due to the per sistency. of vision phenomena, any movement of the object before the lens 31 will be properly transmitted and recorded upon the fluorescent screen 66 and will appear thereupon as a moving image.

to intensify and focus them upon an ordinary,-

system.

The operation of the system when the apparatus used in Fig. 3 is employed at the transmitting station is very similar to that already described. The cathode beam covers the area of the fluorescent screen I5 under the influence of the magnetic and electrostatic fields. When the beam is at one particular point, the light from that spot will traverse the film 18, lens 11 and photoelectric cell Iii.

The variation of current of the photoelectric cell 16 causes the carrier frequency to be'modulated in accordance with the current flow which is directly proportional to the intensity of light from the fluorescent spot that reaches the photoelectric cell. As this condition occurs for each scribed. The method of reproduction is the same as has been explained in conjunction with Figs. 1 and 2.

The intensity of the cathode beam may be regulated by regulating the voltage of the alternating-current sources ll or 62 in a well known manner.

- Attention is drawn to the fact that any change in the frequency of operation of the alternatingcurrent generators 22 and 23 at the transmitting station causes a corresponding change in the frequency of oscillations in the current affecting the cathode ray at the receiving station, and, consequently, the cathode-ray beams will remain in synchronism at both the transmitting and receiving stations and there will be no distortion in the picture transmitted.

It is obvious that it is entirely possible to have the alternators 22 and 23 generate a synchronizing frequency at a station separate from the transmitting station. In this case the central synchronizing station would be arranged in the manner shown in Fig. 4. The alternators I22 and I23 correspond to the alternators 22 and 23. These altemators serve'to modulate a frequency generated by the oscillating circuit including the,

oscillator triode H8, and this modulated freusual manner.

At the transmitting station in Fig. 5, the operation is the same as has been before described, with the exception that the oscillatory circuit IN is resonant to the synchronizing carrier frequency, and this frequency is transferred to the transformers I05 and I06 of the detector triodes I01 and I08. By the operation of these detectors, the synchronizing frequencies are applied to the coils I08 and H0 and to the plates III and H2. Thefurther operation of the system takes places in the same manner as has been described before.

It will be seen that this arrangement permits a number of transmitting stations to transmit pictures or visual indications with only one central station for generating the synchronizing frequency.

It is, of course, apparent that any number of receiving stations may receive the image broadcasted in a manner similar to that described.

In Fig. 6 I show a modification of my invention in which the cathode ray is projected onto the face of the screen 32' which bears the photoelectric deposit. The screen may comprise an aluminum sheet having a thickness of about half 9. mil and having on at least one side an insulating coating which may, for example, be

1 screen by means of any well known optical produced by oxidation of its surface in a manner well known in the art. The screen 32 may be supported in a highly evacuated vacuumtight container 21' of glass or other suitable material having approximately the form illustrated in Fig. 6. 'As an alternative modification,

the screen 32' may consist of a thin sheet of mica just mentioned.

At the opposite end of a prolongation of the container 21' is positioned an electron source such as an incandescent filament 29' between which and the screen is positioned a tubular anode 3| having an in-leading conductor I52 sealed through the glass walls of the container 21'. As in the Fig. l modification, a metal sheet 30 having a small hole may be interposed between the electron source and the tubular anode, said hole being positioned approximately upon the extension of the axis of the tubular anode. Where such a metallic sheet 30 is used, means may be provided for connecting it through a suitable resistance or a suitable source of potential with the tubular anode 3|.

The electron source 29' and the tubular anode 3| constitute, as in the Fig. 1 modification, a

means for projecting a concentrated stream of' electrons and this electron stream is so directed as to impinge upon a point near the center of the screen .32. tubular anode 3| and the screen 32' may be positioned a pair of deflecting plates 25, 26 similar to those in the Fig. l modification, these plates being adapted to deflect the concentrated electron beam so as to cause the point of its incidence on the screen 3,2 to be varied.

The electron stream is positioned so that its axis, when undefiected, makes an acute angle with the normal to the screen 32'.

The contour of the walls of the container 21 directly in front of the screen and a suitable optical system 31 of a type well known in the art is provided for focusing an image of theview to be transmitted on the side of the screen on which the electron beam firstimpinges. Since the tube wall has a relatively large radius of curvature at the point traversed by the rays of this optical image, the latter can be focused upon the screen with substantially no distortion.

The surface of the screen 32' on which the optical image is focused has disposed upon it by means well known in the photoelectric cell art. a layer 36' of photoelectric material such as potassium. If this potassium is deposited by condensation from the vapor phase, it will produce a layer in the form of separate particles or globules, and the distillation may be continued only until the potassium layer 36' is comparatively thin, that is to say, a layer of the thickness of 10- centimeters will usually be found adequate.

On'the side of the photoelectric screen 32 on At a suitable point between the usually possible to locate this screen in such a position that it is not in the focal plane 01' the optical system, and that accordingly no pronounced shadow of its parts is produced on the photoelectric surface 36'. The collector electrode 39' is connected through a wire I53 sealed through the side of the container 32' to an external circuit which may comprise a source I54 of direct current electromotive force and a resistor I55, the opposite end of the resistor being connected to the lead l5! previously mentioned. An output circuit similar to that connected in Fig. 1 to the electrode 39 and the aluminum plate 34 may be connected across a suitable portion of the resistor.

A magnetic deflecting field may be set up transverse to the path of the electron beam by windings 28 and 29' which are similar to and are supplied with current from an electrical system of the same type as that employed in deflecting the electron beam in Fig. l.

The mode of operation of the arrangement in Fig. 6 is similar to that in Fig. 1. With an image to be transmitted focused upon the screen 32, the electron beam is caused to scan succestenances of the tube in Fig. 6 are so similar to those in Fig. 1 that they will be self-evident to those skilled in the art and no detailed description of them is considered necessary here.

My invention is not limited to the particular arrangement of apparatus illustrated but may be variously modified without departing from the spirit and scope thereof, as set forth in the appended claims.

I claim as my invention:

1; In combination with an electrical condenser comprising a pair of conducting elements sepa-' rated by an insulating gap, said condenser being connected to an electrical circuit in series with a second insulating gap, said circuit being adapted to effectively utilize a' discharge current from said condenser, an electron beam provided with means for normally separating it from contact sively every point on the screen and preferably completes the scanning cycle within a period less than the persistence of human vision. The electrical transmission circuits and other appurwith said gap and for at times moving it to such I a position as to render said gap conductive.

2. In combination with a layer of photo-electric material spaced away from a cooperating electrode within an enclosing chamber, a second conductor separated from said photoelectric material by an insulating gap, an electron beam, and means to deflect said beam alternately to put said gap in a con-conductive and later in a conductive condition.

' VLADIMIR K. ZWORYKIN. 

